1. Field of the Invention
This invention relates, in general, to methods for measuring blood perfusion and, more specifically, to thermal methods for measuring blood perfusion.
2. Description of the Prior Art
Recent advances in the understanding of brain death and major neurologic deficit has enhanced interest in the study of cerebral blood flow. As a result, a wide variety of different techniques or methods have been devised to study and measure cerebral blood flow. Some of the more widely known techniques include an inert gas technique, isotopic scanning and the use of radioactive microspheres. Although somewhat effective, all of these methods have a number of disadvantages.
In the inert gas technique, an inert gas, such as nitrous oxide, is inhaled by the patient. The blood flowing out of the brain is then analyzed to measure the inert gas content and provide an indication of the rate of blood flow through the brain. The isotopic scanning technique is somewhat similar and uses a radioactive gas which is traced by a geiger counter as it flows through the brain, with the measured radioactivity providing an indication of cerebral blood flow. Microspheres utilize small glass beads which are radioactively tagged and traced as they flow through the brain.
However, each of these methods measures blood flow through the entire brain and not in a specific region. As it is well known that different regions of the brain have different blood flow rates, such methods are deficient in providing a localized or regional indication of blood flow or blood perfusion through the capillary bed of an organ. In addition, venous pooling and arterial shutdown during major neurological deficit further distort regional blood flow rates which are not detected by these techniques which only measure blood flow through the entire brain.
Another significant disadvantage of these techniques is that do not lead themselves to rapid repetition. Obviously, the amount of radioactive material which is introduced into the body must be carefully controlled in order to prevent harm to the patient. Thus, extended amounts of time must be provided between each measurement segment utilizing these commonly known blood flow measuring techniques. As a result, rapid changes in blood flow rates during surgery or neurological deficit cannot be detected.
Other blood flow measuring techniques have been devised to measure blood flow in other areas of the human body and in particular through the heart. These techniques utilize electro-magnetic flow meters or thermistors which are placed in the arteries to measure the temperature dilution of the blood as cold water is injected into the arteries. In the latter technique, the temperature dilution can be related to blood flow to provide an indication of blood flow through the heart. However, these technique require large vessels, such as arteries or veins, which prevents their use in measuring cerebral blood flow where the arteries and veins are too small for the metering apparatus.
Thus, it would be desirable to provide a method for measuring blood perfusion which overcomes the problems of similar prior art methods. It would also be desirable to provide a method for measuring blood perfusion which may be quickly repeated without danger to the patient. It would also be desirable to provide a method for measuring blood perfusion which provides a measurement of blood perfusion in a particular localized region of an organ of the patient. It would also be desirable to provide a method for measuring blood perfusion which is both simple and inexpensive to use. Finally, it would be desirable to provide a method for measuring blood perfusion which is ideally suited for measuring cerebral blood perfusion.